Welding assembly for friction stir welding

ABSTRACT

The invention relates to a welding assembly for joining together workpieces ( 1, 2 ) along a joint between said pieces by means of friction stir welding. The welding assembly comprises a welding probe ( 9 ) intended to be advanced along said joint during the welding operation. The welding probe comprises a body ( 10 ) and a pin ( 20 ), the body being arranged to be pressed against the upper faces of the workpieces during the welding operation whereas the pin is arranged to be moved along said joint during the welding while being rotated and pressed against said workpieces. The pin ( 20 ) and the body ( 10 ) are also so arranged relative to one another as to be mutually movable, allowing said pin and said body to perform different movement patterns relative to one another.

This is a national phase filing of International Application No.PCT/SE98/00861, filed May 12, 1998 that was published in English, andclaims priority under 35 U.S.C. §119 for Swedish Application No.9701865-9 filed May 16, 1997, and U.S. Provisional Application No.60/047,133 filed May 20, 1997.

The present invention relates to a welding assembly for joining togetherworkpieces along a joint between said pieces by means of friction stirwelding, said welding assembly comprising a welding probe intended to beadvanced along said joint during the welding operation and comprising abody and a pin, the body being arranged to be pressed against the upperfaces of the workpieces during the welding operation whereas the pin isarranged to be moved along said joint during the welding while beingrotated and pressed against said workpieces.

The definition friction stir welding designates a welding methodaccording to which the workpieces to be joined together are plasticizedalong their joint line by supply of frictional heat from a rotatingwelding probe, said probe being moved along the joint between theworkpieces while at the same time being pressed against the workpieces.As described in WO93/10935 and WO95/26254 the welding probe should bemanufactured from a material that is harder than that of the workpieces,and during the welding operation the workpieces should be securely fixedrelative to one another and to the work-table. In this respect thistechnique differs from that of conventional friction welding accordingto which the frictional heat is generated by the relative motion of theworkpieces as they are being pressed together, i.e. the frictional heatis generated only by the two components to be joined together. Thisfriction stir welding technique according to the above-mentionedpublications may be used for the welding of different materials, such asplastics, metals, etcetera in various fields of application, for exampleto join workpieces together, to repair cracks in a workpiece, and so on.The design of the welding probe is conditioned e.g. by the material tobe welded and by the intended application.

One of the problems encountered in the implementation of the weldingmethod described in the above patent specifications for joining togethere.g. aluminium profile sections is that vertically, the welding probe inprinciple must extend through the entire joint between the workpieces tobe welded together in order to ensure that the resulting weld willextend all the way from the top to the lower faces of the workpieces,i.e. that a complete-penetration weld is produced. The welding probesdisclosed in the above patent specifications are in the form of arotatable, essentially cylindrical body the upper part of which isconnected to a drive unit and the lower part of which is provided with aco-rotating pin. The essential difference distinguishing the probeaccording to WO93/10935 from that of WO95/26254 is that according to theformer the body and the pin of the probe form one integral piece whereasaccording to the latter they are two separate pieces. In accordance withthe latter patent specification the body and the pin are, however,securely interconnected during the welding operation proper.Accordingly, the entire welding probe or at least the pin thereof mustbe exchanged according to the latter specification in order to allowworkpieces of different thicknesses to be welded together.

An additional problem is that the thickness of the workpieces to bejoined together may vary along the joint, and consequently the endproduct will not be formed with a weld that extends all the way throughthe joint, i.e. the joining-together operation will not result in anacceptable weld.

A further problem encountered in prior-art welding probes is theformation of an exit aperture at the point where the probe is lifted offthe produced weld following completion of the welding operation.

Another problem is that presently existing welding probes precludes anysupply of additional material during the welding operation proper, whichsupply is desirable when one wishes that the body be pressed against thetop faces of the workpieces without the lower part of the body, i.e. itsso called shoulder, entering into the workpieces.

One object of the present invention thus is to provide a weldingassembly to be used for friction stir welding operations that in aconvenient and rapid manner may be adapted to different thicknesses inthe workpieces to be joined together or may adjust itself to thicknessvariations in the workpieces.

A further object of the present invention is to provide a weldingassembly of the kind referred to which allows supply of additionalmaterial during the welding operation.

These objects are achieved in accordance with the present invention in awelding assembly for use in friction stir welding of the kind defined inthe introduction, which probe is characterised in that the pin and thebody are so arranged relative to one another as to be mutually movable,allowing said pin and body to perform different movement patternsrelative to one another.

As a consequence of the probe of the welding assembly being constructedin the form of a pin and a body that are so disposed relative to oneanother as to be mutually movable, whereby they are allowed to performmutually different movement patterns, any material that is plasticizedduring the welding operation will be safely retained below the lowerpart of the body, and consequently the position of the pin relative tothe joint may be adjusted in a manner ensuring that acomplete-penetration weld will be produced in the full extension of thejoint.

Advantageous modified embodiments of this welding assembly are definedin the dependent claims.

The invention will be described in more detail in the following withreference to the accompanying drawings, wherein

FIG. 1 is a lateral view of an apparatus designed for friction stirwelding and comprising a welding assembly in accordance with the presentinvention.

FIG. 2 is a cross-sectional view on an enlarged scale of a firstembodiment of a welding probe incorporated in said welding assembly.

FIG. 3 is a cross-sectional view on an enlarged scale of a secondembodiment of the welding probe.

FIG. 4 is a section taken on line IV—IV through the welding probe shownin FIG. 3.

The device illustrated in FIG. 1 is intended to be used to join togethertwo workpieces 1, 2 in the form of e.g. two extruded aluminium profilesections by means of friction stir welding. The device comprises awork-table having a backing bar 4 in the form of an I-beam, ahorizontally extending machine table 5 and a stationary, rigid frame 6.The device also comprises a number of clamping means 7 and 8 designed toclampingly secure the workpieces 1 and 2 to one another and to thework-table 3 during the welding operation. Each clamping means 7 and 8could be a pressure element that is connected to a pressure cylinder.The device likewise comprises a welding assembly formed with a weldingprobe 9 and a drive unit, not shown, to advance the welding probe alongan existing joint between the workpieces.

As most clearly apparent from FIG. 2, the welding probe 9 is formed asan essentially conical rotationally symmetrical body 10 having an innercavity 11 and an end-to-end bore 12 disposed in the center of the lowertapering end 10 a of the body. Owing to its appearance, this end 10 awill be referred to in the following as the shoulder. The outer portionof the shoulder is configured with a concave bottom face 13 at thecentre of which debouches the bore 12. At the upper enlarged end of thebody 10, a bearing 15 rotationally interconnects the body and aintermediate member 14. This intermediate member 14 is provided at itsupper end with two pivot pins 16, each mounted in a fork-shaped support17 designed to lower and raise the intermediate member, and consequentlythe body 10, vertically. The intermediate member 14 is also formed witha cavity 18 which debouches into the cavity 11 of the body 10.

A rotary spindle 19 at the lower end of which is mounted a conicallyshaped threaded pin 20 is housed in the cavities 18 and 11 in such amanner that the pin 20 protrudes from the bore 12 in the shoulder lOa. Acircumferential bearing 21 interconnects the spindle 19 and theintermediate member 14 and opposite the widened part l0 b of the body 10the spindle 19 supports an exterior gear ring 22. The widened part l0 blikewise supports an interior gear ring 23 on the upper part of itsinner face, said gear ring 23 being in contact with the exterior gearring 22 by means of a number of free-running gear wheels 24, forinstance six such wheels. Owing to this arrangement,. the spindle 19 isable to rotate the pin 20 as well as the shoulder l0 a, although atdifferent rotational speeds, depending on the number of teeth on thegear rings 22 and 23, and in opposite directions.

As likewise appears from the drawing figure a supply means 25 isprovided in the form of an elongate pipe extending through theintermediate member 14 and the cavity 11 of the body 10 so as to debouchexactly above the bore 12. At its lower end,. the pipe is bent at anangle to allow it to be accommodated between the inner upper part of theshoulder and the lower conically shaped end of the spindle.

From FIG. 1 likewise appears that the body shoulder 10 a is urgedagainst the top faces of workpieces 1 and 2 during the weldingoperation, whereas the pin 20, while rotating, is advanced in the jointwhile being pressed against the workpieces.

The welding probe 9 in accordance with the embodiment of FIGS. 3 and 4,like that of FIG. 2, consists of a rotary spindle 30 on the lower partof which is mounted a rotary threaded pin 31. However, the body 32 isasymmetrical and is not arranged to rotate but to oscillate relative tothe pin 31. As also appears from FIG. 4. the body is in the shape of acone from the lower part of which a portion has been removed to form alower shoulder-like end 32 a. The body is also formed with an internalcavity 33 and an upper widened end 32 b. At its lower end the shoulderis configured so as to comprise a concave bottom 34 into the centre ofwhich debouches a bore 35. Like in accordance with the previousembodiment, the pin 31 protrudes from this bore.

At its upper widened end 32 b the body is rotatably connected to astationary intermediate member 40 by means of a bearing 36.

As likewise appears from FIG. 3 a supply means 37 in the shape of anelongate pipe is provided, said pipe extending through the intermediatemember 40 and the cavity 33 of the body 32 so as to debouch exactlyabove the bore 35. The lower pipe end is bent at an angle to allow it tobe accommodated between the inner upper part of the shoulder and thelower conically shaped end of the spindle.

As appears particularly from FIG. 4, the upper right-hand part of thebody 32 is provided with a link 38 the opposite end of which isconnected to a rotary eccenter shaft 39. Owing to this arrangement, thebody 32 may be given an oscillating motion in the horizontal planerelative to the top faces of the workpieces 1 and 2 instead of a rotarymotion, as is the case in the first embodiment. However, both motionswill cause frictional heat to generate between the shoulder and the topfaces of the workpieces. Also in this case it is possible to mount acutting tool on the oscillating shoulder for the purpose ofpost-treating the welded surface.

When the workpieces 1 and 2 are to be joined together by means offriction stir welding, the workpieces 1 and 2 are initially secured bymeans of the clamping means 7 and 8, care being taken that the joint,i.e. the air gap, between the facing end edges of the workpieces doesnot exceed dimensions that are liable to cause a deficient weld to form.A drive motor, not shown, then causes the spindle 19 or 30 to rotatewhile at the same time the entire welding probe 9 is made to move at apredetermined speed along the joint, propelled by the above mentioneddrive unit. Also the body 10 will be made to rotate in the oppositedirection of rotation as the pin 20 but at a different speed. Asmentioned previously, the body 32 will instead perform an oscillatingmotion. Thus, the pin and the body, in accordance with both embodiments,are arranged in such a manner relative to one another as to move indifferent motion patterns during the welding operation. The frictionalheat generated by the motions of the body and the shoulder will, asdescribed initially, cause the end edges of the workpieces to plasticizewhile at the same time they are secured by the clamping means 7 and 8.

In order to achieve a complete-penetration weld along the entire joint,irrespective of varying thicknesses in the workpieces to be joinedtogether, a servo mechanism, not shown, is connected to the weldingprove in such a manner as to cause the relative positions between thepin and the shoulder to vary vertically in response to said thicknessvariations, ensuring that in principle the pin extends through theentire joint for the duration of the welding operation, i.e. that thedistance by which the pin protrudes below the shoulder corresponds tothe depth of the joint. The different movement patterns of the shoulderand the pin, respectively, ensure that any material that is plasticizedby the frictional heat is safely retained underneath the shoulder and isprevented from entering into the bore 12 or 35 between the pin and theshoulder, and as a result the position of the pin vertically may changewithout problem during the entire welding operation.

The external threading of the pins 20 and 31 causes the material that isplasticized during the welding operation by the frictional heatgenerated during that operation to flow in the longitudinal direction ofthe pin, so called pumping effect. In accordance with the firstembodiment this pumping effect is enhanced owing to the rotation of thebody and the pin in opposite directions. The pumping effect is furtherimproved if in addition thereto the bore 12, respectively, of the bodiesare threaded. This pumping effect in combination with theabove-described relative motion of the pin and the shoulder also makesit possible to feed added material that is supplied to the upper mouthsof the bore 12, respectively, down through the shoulder and into thejoint to provide surplus material when the material of the workpieces assuch is insufficient, either to fill the exit crater formed when the pinis lifted off the formed weld at the end of the welding operation, or tobe supplied between the top faces of the workpieces and the shoulder, orto prevent the shoulder from entering into the top faces of theworkpieces. In the latter case the body, like in the previouslydescribed case, is pressed against the top faces of the workpieces butvia added intermediary material.

In order to prevent the material that is plasticized during the weldingoperation from producing a permanent bond between the body and the pinon cooling following the welding operation, the body and the pin areinterconnected in such a manner as to be coaxially displaceablevertically relative to one another. Either the pin may be lifted off thebore in the shoulder after each individual welding operation or else theupper pin end which is connected to the spindle may be formed with aneck portion having a considerably smaller diameter than said bore, anarrangement which prevents weld metal from bonding the parts togetherduring the cooling step.

In order to obtain the desired welding temperature more rapidly it ispossible to supply extra heat prior to and/or during the weldingoperation. It is likewise possible to supply the body and/or the pinwith extra heat during and/or after the welding operation to preventthat the body and the pin from being permanently bonded to one anotherby the plasticized material that forms during the welding operation.

It should be appreciated that the invention is not limited to theembodiment described and shown herein but could be modified in a varietyof ways within the scope of the appended claims. For example, the bodyand the pin could be arranged to rotate in the same direction at thesame or at different speeds. Alternatively, the body and the pin couldbe arranged to rotate at the same mean speed but in pulsating rotarymode, making relative motions between the body and the pin possibleduring substantially the entire welding operation. The differentiatedmotion patterns could also be achieved by making the body immobile, i.e.stationary, during the welding operation. In this case it is necessaryto heat the body electrically or with the aid of a heat-carrying mediumto compensate for the heat lost because in this case the stationary bodydoes not produce any frictional heat. Also when the body is notstationary, e.g. oscillates, it may be necessary to supply additionalheat because the produced frictional heat may not be sufficient tosatisfactorily plasticize the end edges of the workpieces.

What is claimed is:
 1. A welding assembly for joining togetherworkpieces (1, 2) along a joint between said pieces by means of frictionstir welding, said welding assembly comprising a welding probe (9)intended to be advanced along said joint during the welding operationand comprising a body (10; 32) and a pin (20; 31), the body beingarranged to be pressed against the upper faces of the workpieces duringthe welding operation whereas the pin is arranged to be moved in saidjoint during the welding while being rotated and pressed against saidworkpieces, characterised in that the pin (20; 31) and the body (10; 32)are so arranged relative to one another as to be mutually movable,allowing said pin and said body to perform different movement patternsrelative to one another.
 2. A welding assembly as claimed in claim 1,characterised in that the pin (20; 31) is arranged to rotate in anend-to-end bore (12; 35) in the body (10; 32) in such a manner that thedistance by which the pin is allowed to protrude below the bodycorresponds to the depth of the joint in each point along the jointduring the entire welding operation.
 3. A welding assembly as claimed inclaim 1, characterised in that the pin (20; 31) has external threads inorder to allow a flow directed in the longitudinal direction of the pin,so called pumping effect, of the material that is plasticized during thewelding operation by the frictional heat generated during thatoperation, and/or of any additional material that is arranged to besupplied to the joint.
 4. A welding assembly as claimed in claim 1,characterised in that also the body (10; 32) is rotatable during thewelding operation.
 5. A welding assembly as claimed in claim 1,characterised in that the body (10; 32) and the pin (20; 31) arearranged to rotate in opposite directions and/or at different speedsrelative to one another.
 6. A welding assembly as claimed in claim 1,characterised in that the body (10; 32) and the pin (20; 31) arearranged to rotate at the same mean rotational speed but in a pulsatingrotary mode, whereby a relative movement between the body and the pinmay be obtained during substantially the entire welding operation.
 7. Awelding assembly as claimed in claim 1, characterised in that the body(10; 32) is arranged to oscillate during the welding operation.
 8. Awelding assembly as claimed in claim 1, characterised in that the body(10; 32) is stationary during the welding operation.
 9. A weldingassembly as claimed in claim 1, characterised in that the body (10; 32)is arranged to be heated by supply of external energy in order toprovide heat necessary to the welding operation in addition to thefrictional heat generated by the pin (20; 31) during the weldingoperation.
 10. A welding assembly as claimed in claim 1, characterisedin that the body (10; 32) and the pin (20; 31) are interconnected insuch a manner as to be coaxially displaceable relative to one another toallow the pin and the body to so move relative to one another after thewelding operation that any plasticized material that forms during thewelding operation is prevented from forming a permanent bond betweenbody and pin during cooling following the welding operation.
 11. Awelding assembly as claimed in claim 1, characterised in that additionalheat is supplied to the body (10; 32) and/or to the pin (20; 31) priorto and/or during the welding operation to more rapidly achieve thedesired welding temperature.
 12. A welding assembly as claimed in claim1, characterised in that additional heat is supplied to the body (10;32) and/or to the pin (20; 31) during and/or after the welding operationto prevent plasticized material that forms during the welding operationfrom forming a permanent bond between the body and the pin.
 13. Awelding assembly as claimed in claim 2, characterisedin that additionalmaterial is arranged to be supplied to the joint and/or to the top facesof the workpieces (1, 2) by means of a supply means debouching adjacentthe bore (12; 35) formed in the body.
 14. A welding assembly as claimedin claim 7, characterised in that a tool designed for working on theproduced weld joint surface is attached to the rear part of the body(10; 32).
 15. A welding assembly as claimed in claim 2, characterised inthat the pin (20; 31) has external threads in order to allow a flowdirected in the longitudinal direction of the pin, so called pumpingeffect, of the material that is plasticized during the welding operationby the frictional heat generated during that operation, and/or of anyadditional material that is arranged to be supplied to the joint.
 16. Awelding assembly as claimed in claim 2, characterised in that also thebody (10; 32) is rotatable during the welding operation.
 17. A weldingassembly as claimed in claim 3, characterised in that also the body (10;32) is rotatable during the welding operation.
 18. A welding assembly asclaimed in claim 2, characterised in that the body (10; 32) and the pin(20; 31) are arranged to rotate in opposite directions and/or atdifferent speeds relative to one another.
 19. A welding assembly asclaimed in claim 3, characterised in that the body (10; 32) and the pin(20; 31) are arranged to rotate in opposite directions and/or atdifferent speeds relative to one another.
 20. A welding assembly asclaimed in claim 2, characterised in that the body (10; 32) and the pin(20; 31) are arranged to rotate at the same mean rotational speed but ina pulsating rotary mode, whereby a relative movement between the bodyand the pin may be obtained during substantially the entire weldingoperation.
 21. A welding assembly as claimed in claim 2, characterisedin that the body (10; 32) is arranged to oscillate during the weldingoperation.